PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 
785 
from the inner side near its termination in the hind lobe a short and low ridge of enamel 
passing downward, forward, and inward to be lost in the inner division of the transverse 
valley. There is likewise a small vertical ridge of enamel from the fore part of the 
hind lobe, internal to the link and its accessory process, which ridge descends straight 
to the bottom of the valley. These productions of enamel cause corresponding com- 
plexities of the grinding-surface, which are correlatively associated with the more massive 
bone wielding the grinding-instruments. 
On the inner surface of this portion of mandible (Plate LXXVI. fig. 8) the super- 
angular channel (ib. b ) is shorter, deeper, defining a narrower and shorter beginning of 
the inflected angle than in Macrojpus , the channel commencing anteriorly at a vertical 
parallel with the interval between the last and penultimate molars. By the above- 
defined characters I infer from the present fossil a distinct subgenus of Macropodidce , for 
which the massiveness of the mandible in proportion to the teeth it supports has suggested 
the name above given. 
§ 4. Leptosiagon * gracilis, Ow. — On similar grounds the present genus and species 
of extinct Kangaroo are based upon a portion of a right mandibular ramus with m \ and 
m 2 in place, part of the socket of m s, and the whole of that of d 4, from which the tooth 
appears to have been naturally shed or worn away (Plate LXXVI. figs. 11-15). The 
transverse fracture of the mandible anterior to d 4 (ib. fig. 15) shows the bone to be 
unusually thin in proportion to its depth ; the partial thickening on the inner side is 
almost ridge-like ; the outer thickening, beginning opposite the inner one, is continued 
with a convex curve to the lower border of the ramus. 
The distinctive dental character of the present subgenus is in the sculpturing of the 
hind surface of the molars (ib. fig. 14) ; two slender well-defined pyramids of enamel, 
in high relief, rise from the base of that surface at its inner half, and terminate in 
points, the inner one within a line of the unworn summit of the hind lobe, the outer 
one within two lines of the same. A deep reversed, narrow, angular or pyramidal 
notch divides the inner pyramid from the inner side of the hind lobe, a deeper notch of 
corresponding form divides the inner from the outer pyramid, and a fainter, narrow, 
short, linear groove separates the outer pyramid from the rest of the outer part of the 
hind surface, which is continued by a bold convexity into the outer side of the molar. 
The outer end of both transverse lobes incline more forward than in Macropus Titan ; 
but, as in that species, the outer bases of the two lobes meet to define an acute-angled 
pointed lower termination of the interval or valley there (ib. fig. 11, mi, m 2 ). In 
Sthenurus and Protemnodon the lower termination of the same interspace is rounded, 
not pointed, the outer bases of the lobes not being in the same degree extended antero- 
posteriorly. 
There is no accessory ridge from the inner side of the mid link ; but in the smaller 
outer part of the hollow between the front lobe and the prebasal ridge, defined by the fore 
link, there is in m 2 a vertical enamel ridge : it is not present in m 1 (Plate LXXVI. fig. 13). 
* From Xeirros, slender ; trtayibv, jaw-bone. 
5 n 2 
